Locking devices are already known for locking together a first tube and a second tube, said first tube being configured to slide inside said second tube when the locking device is deactivated. By activating said locking device, it is possible, conversely, to prevent the first tube from sliding relative to the second tube. Such locking devices are, in particular, implemented on bicycles between the saddle post, at the top end of which a saddle is arranged, and the saddle tube arranged on the frame of the bicycle, so as to adjust the height positioning of the saddle.
The international patent application published under the number WO 2009/027681 A1 discloses a locking device comprising a rod arranged longitudinally inside a first tube that consists of a saddle post and that is slidably mounted inside a second tube consisting of a saddle tube, and a cam actuation system making it possible to move said rod in translation along the longitudinal axis of said first tube. That locking device further comprises a first plate arranged at the bottom end of the first tube, a second plate being mounted to slide relative to the first plate along the longitudinal axis of the first tube, that second plate being secured to the bottom end of the rod. The first plate and the second plate are spaced apart by gap that can be varied under the action of the rod. Inside the gap, i.e. between the first and second plates, there is provided an elastically deformable annular plug that, in a rest position, has an outside diameter that is slightly smaller than the inside diameter of the second tube so as to enable said elastically deformable plug and the first tube to slide inside the second tube. By acting on that rod, via the actuation system, it is possible to reduce the gap between the first plate and the second plate, thereby acting on the elastically deformable plug and making it possible to increase the outside diameter of said elastically deformable plug so that it has an outside diameter greater than the inside diameter of the second tube. That makes it possible to compress said elastically deformable plug against the inside face of the second tube, and thus to lock the relative position between the first tube and the second tube.